The present proposal represents a pilot project designed to generate preliminary information regarding the genetic basis for the aciduricity of Streptococcus mutans. Mutants defective in aciduricity will be sought utilizing a novel Tn9l6 mutagenesis system. The mutants will be characterized biochemically and those defective in both acid tolerance and transformability used to isolate and identify the mutated gene(s). The genes involved will be characterized in detail in an investigation supported by a subsequent application derived from these studies. Since acidurity appears to be an important cariogenic property of S. mutans, the approach proposed should further our understanding of the molecular basis for this important caries related trait. Such information could serve as a basis for designing strategies to neutralize aciduricity in these organisms and further reduce the incidence of caries in humans.